The present invention relates to a sheet feeding apparatus for transporting sheets such as a plastic film and, more particularly, relates to a transport roller configuration for transporting sheets in a predetermined direction without damaging the sheets and an image reading apparatus such as a scanner apparatus or copier apparatus equipped with the sheet feeding apparatus.
Generally, a sheet transport apparatus and an image reading apparatuses equipped with a sheet transport apparatus consecutively transport sheets, and include various devices, i.e. a sheet supply unit, sheet processing unit and sheet discharge unit such as a copier, a printing machine or a paper currency handling apparatus, as disclosed, for example, in Japanese Patent Publication (Kokai) No. 08-225221. A variety of methods such as a vacuum transport method, an endless belt method, and a roller method have been used for transporting sheets. As a simple transport mechanism, a pair of rollers may be used for nipping and transporting sheets.
The present invention relates to a structure having a pair of rollers for nipping and transporting sheets. Conventionally, as a method of transporting sheets using a drive roller and a follower roller contacting each other, there have been a structure using one roller positioned at the center of the sheets, and another structure having more than two rollers arranged in a width direction of the sheets. When a plurality of sheets having different widths is transported, the latter method has been primarily used.
In the structure having a plurality of rollers to transport the sheets, there are problems of causing the sheets to be wrinkled or dirty. In order to transport the sheets with high precision without slipping, it is necessary to firmly nip the sheets with a pair of drive and follower rollers. When the sheets are firmly nipped for transport, it is well known that two (or more) rollers arranged in the sheet width direction may apply unequal pressure to the sheets, thereby causing wrinkle or stain in the sheets or generating unusual sounds in-the system.
Japanese Patent Publication (Kokai) No. 08-225221 has disclosed a method in which rollers transport sheets in different width directions to remove a wrinkle. In this method, a roller positioned at the center is aligned in the transport direction and rollers positioned at left and right sides are aligned outwardly to apply an outward force to the sheets, thereby preventing wrinkle.
In the conventional method disclosed in Japanese Patent Publication (Kokai) No. 08-225221, the rollers have various outer diameters or separate rotating shafts offset in different directions, so that a plurality of the rollers is aligned in different directions. Accordingly, it is difficult to form the rollers, and the structure becomes complex.
In view of the problems described above, an object of the present invention is to provide a sheet transport apparatus in which a plurality of rollers arranged in a width direction has a transporting force in different directions with a simple structure, thereby preventing wrinkle or stain in sheets and unusual sounds.
Another object of the present invention is to provide an image reading apparatus in which wrinkle and unusual sounds are eliminated when sheets are registered.
Further objects and advantages of the invention will be apparent from the following description of the invention.